The present invention relates to a hydraulic brake system for automotive vehicles with a master brake cylinder and with a hydraulic power booster connected upstream of the master brake cylinder. An electromotively drivable pressure medium pump is employed for providing auxiliary hydraulic energy. The drive of the pump may be switched on by a contact of a pressure accumulator, on the one hand, and by a brake pedal contact, on the other hand, wherein, in the unbraked operation of the automotive vehicle, the pressure accumulator is permanently kept on a pressure level sufficient for an initial actuation of the brake. A valve assembly is provided which permits a connection between the outlet of the pressure medium pump and the port of the power booster.
Hydraulic brake systems for automotive vehicles of the type described are known. In these systems, a hydraulic pressure accumulator with a relatively small accumulator volume serves to make available auxiliary hydraulic energy in the initial phase of braking. After this initial phase of braking in respect of the energy supply has been bridged by the pressure medium stored in the pressure accumulator, the actual energy supply of the hydraulic power booster will be effected by an electromotively driven pressure medium pump which, at this point of time, delivers a medium flow or, respectively, generates a hydraulic pressure which largely corresponds to the hydraulic pressure in stationary operation.
Another component part of the known brake systems is a hydraulically controllable valve which can be governed by the hydraulic pressure in the pressure chamber of the hydraulic power booster. In each initial phase of braking, said valve is switched by the pressure developing in the pressure chamber of the hydraulic power booster to assume a position in which there is interruption of a connection between the outlet of the pressure medium pump and the hydraulic pressure accumulator. Upon each brake actuation, first the pressure accumulator is discharged via the valve to the pressure chamber of the hydraulic power booster.
The essential advantage of the known systems is that the pressure medium pump is in permanent operation during braking only. Apart from that, the drive of the pressure medium pump is switched on only if the pressure prevailing in the pressure accumulator drops below a predeterminable valve. It follows that the brake system necessitates a relatively low electric energy consumption and that the auxiliary hydraulic energy required is available already at the commencement of braking. The difficulties arising in the start-up phase of the pressure medium pump in respect of its delivery will become inapplicable by use of the pressure accumulator.
In the device described, the pressure-controlled valve is of relatively complicated design and therefore incurs corresponding manufacturing and assembling costs. It is therefore an object of the present invention to considerably simplify a device of the species initially referred to.